Chapter 37. Upgrading Your Current System
This chapter explains the various methods available for upgrading your Red Hat Enterprise Linux system.
37.1. Determining Whether to Upgrade or Re-Install
Although anaconda provides an option for upgrading from earlier major versions of Red Hat Enterprise Linux to Red Hat Enterprise Linux 6, Red Hat does not currently support this. More generally, Red Hat does not support in-place upgrades between any major versions of Red Hat Enterprise Linux. (A major version is denoted by a whole number version change. For example, Red Hat Enteprise Linux 4 and Red Hat Enterprise Linux 5 are both major versions of Red Hat Enterprise Linux.)
In-place upgrades across major releases do not preserve all system settings, services or custom configurations. Consequently, Red Hat strongly recommends fresh installations when upgrading from one major version to another.
While upgrading from Red Hat Enterprise Linux version 4 Update 4 is technically possible, you are more likely to have a consistent experience by backing up your data and then installing this release of Red Hat Enterprise Linux 6 over your previous Red Hat Enterprise Linux installation.
To upgrade from Red Hat Enterprise Linux 4 you should bring your system up to date using RHN before performing the upgrade.
This recommended reinstallation method helps to ensure the best system stability possible.
If you currently use Red Hat Enterprise Linux 4 Update 4, you can perform a traditional, installation program-based upgrade.
However, before you chose to upgrade your system, there are a few things you should keep in mind:
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Individual package configuration files may or may not work after performing an upgrade due to changes in various configuration file formats or layouts.
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If you have one of Red Hat's layered products (such as the Cluster Suite) installed, it may need to be manually upgraded after the Red Hat Enterprise Linux upgrade has been completed.
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Third party or ISV applications may not work correctly following the upgrade.
Upgrading your system installs updated versions of the packages which are currently installed on your system.
The upgrade process preserves existing configuration files by renaming them with an .rpmsave extension (for example, sendmail.cf.rpmsave). The upgrade process also creates a log of its actions in /root/upgrade.log.
As software evolves, configuration file formats can change. It is very important to carefully compare your original configuration files to the new files before integrating your changes.
It is always a good idea to back up any data that you have on your systems. For example, if you are upgrading or creating a dual-boot system, you should back up any data you wish to keep on your hard drives. Mistakes do happen and can result in the loss of all of your data.
Some upgraded packages may require the installation of other packages for proper operation. If you choose to customize your packages to upgrade, you may be required to resolve dependency problems. Otherwise, the upgrade procedure takes care of these dependencies, but it may need to install additional packages which are not on your system.
Depending on how you have partitioned your system, the upgrade program may prompt you to add an additional swap file. If the upgrade program does not detect a swap file that equals twice your RAM, it asks you if you would like to add a new swap file. If your system does not have a lot of RAM (less than 256 MB), it is recommended that you add this swap file.
